The present invention relates to a printing ink, and specifically a pigmented ink for marking porous media.
Ink-jet printing systems have been developed to provide high speed and high quality printing. These printing systems can provide precise printed images quietly, accurately, and at low cost. Drop on-demand systems (or pressure pulse systems) and thermal ink-jet systems are two ink-jet systems that use different methods to eject ink. In these ink-jet printing systems, liquid inks and solid, "hot melt" inks have been developed. "Hot melt" inks are inks which are typically in a solid form at room temperature, but which change to a liquid at an elevated temperature above the room temperature. Hot melt ink technology can be used to print images on many different types of media. The liquid inks are fluid at room temperature. Water-based inks employ water as a primary solvent and oil-based inks employ an organic solvent as a main solvent.
Because the liquid inks are fluid at room temperature, printed images from the inks tend to feather when printed on a porous medium, such as a corrugated container or Kraft paper, limiting the print density and clarity that can be achieved. Hot melt oil-based ink-jet ink compositions, which are solid at room temperature and melt upon heating, can produce smaller dot sizes and reduced smearing because the ink hardens rapidly. If the ink is not hard enough, smear may remain. It is important to maintain both the speed and the quality of printing by adjusting the properties of the printing ink. Dot size and edge definition can be adversely affected when printing on porous media, due in part to bleeding and smearing of the printed image.